1. Technical Field
The present application relates generally to a radio communication system and, in particular, to a device and method for controlling a display to suppress noise generated from the display in a radio communication system.
2. Description of the Related Art
In general, a radio communication system includes a display consisting of a multiplicity of displaying elements to display the operating status thereof. Typically, the display comprises either a plurality of LEDs (Light Emitting Diodes) or seven-segment displays, which are turned on and off at specified intervals to indicate an operating status of the radio communication system. In particular, the display typically includes separate displaying elements for indicating a normal operating status and for indicating an abnormal operating status. These displaying elements operate by flickering at stated periods so as to indicate either the normal or abnormal operating status.
Referring now to FIG. 1, a diagram illustrates a display control device of a radio communication system. The display control device includes a microprocessor 10, a first displaying element LED1 and a second displaying element LED2. For the convenience of explanation, it is assumed that LED1 and LED2 of FIG. 1 are utilized for indicating a normal operating status of the system. For example, the first displaying element LED1 can be used for indicating a normal operating status of one part of a radio communication system and the second displaying element LED2 can be used for indicating a normal operating status of another part of the system. As illustrated, LED1 comprises an anode which is connected to a supply voltage Vcc via a resistor R1, and a cathode which is connected to a collector of a first NPN transistor Q1 (which operates as a switching element). The first transistor Q1 includes an emitter which is connected to ground and a base which is connected to the microprocessor 10 via a current limiting resistor R3. A first control voltage Vo1 is generated by the microprocessor 10 and applied to the base of transistor Q1.
Similarly, LED2 comprises an anode which is connected to the supply voltage Vcc via a resistor R2, and a cathode which is connected to a collector of a second NPN transistor Q2 (which also operates as a switching element). The second transistor Q2 has an emitter which is connected to ground and a base which is connected to the microprocessor 10 via a current limiting resistor R4. A second control voltage Vo2 is generated by the microprocessor 10 and applied to the base of transistor Q2. The microprocessor 10 controls the first and second transistors Q1 and Q2 via the first control voltage Vo1 and second control voltage Vo2, respectively, so as to activate and deactivate (i.e., turn on and off) LED1 and LED2.
When the system operates normally, LED1 and LED2 will flicker on and off in accordance with the respective control voltage waveforms illustrated in FIGS. 2A and 2B to indicate a normal operating status. In particular, the microprocessor 10 outputs the first control voltage Vo1 (shown in FIG. 2A) and the second control voltage Vo2 (shown in FIG. 2B) in rectangular waveforms. When the respective parts of system corresponding to LED1 and LED2 operate normally, LED1 and LED2 are simultaneously activated and deactivated at the same time periods (in accordance with the waveforms of FIGS. 2A and 2B, respectively). Consequently, LED1 and LED2 will generate noise frequencies as shown in FIGS. 3A and 3B, respectively.
Specifically, FIG. 3A illustrates noise frequencies that are generated when LED1 is activated and deactivated in accordance with the first control voltage Vo1 of FIG. 2A. Similarly, FIG. 3B illustrates noise frequencies that are generated when LED2 is activated and deactivated in accordance with the second control voltage Vo2 of FIG. 2B. Theoretically, the noise frequencies generated from LED1 and LED2 have infinite harmonics. In addition, since the frequencies generated by the activation/deactivation of LED1 and LED2 are in phase, the noise frequencies will constructively interfere with each other, thereby amplifying the noise signals of the respective frequency components.
The problem with these resultant noise frequencies is that they have an influence upon the communication quality of a radio communication system such as a TDMA (Time Division Multiple Access) communication system and, especially, a DECT (Digital European Cordless Telephone) system. In addition, notwithstanding that the noise frequencies generated from the respective LEDs may have a slight phase difference, some harmonics may have the same frequencies. Consequently, similar frequency components will constructively interfere with each other, thereby amplifying the noise signals having similar frequencies. Unfortunately, these noise signals can deteriorate the communication quality of the radio communication system.